Sagebrush Ecosystems of the West

Adam worked as a plant-focused biological technician all over the southwestern US, then got his PhD at the University of Colorado Boulder in Jennifer Balch’s lab. He is currently a postdoctoral research ecologist at the USDA-ARS in Fort Collins, and studies fire ecology, plant community ecology and invasion ecology.

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Science Moab: Can you paint a picture of the sagebrush for us?

Mahood: Sagebrush is actually a whole biome, the largest biome in the Western US. Sagebrush ecosystems are really widespread; you’ll hear people refer to it as the sagebrush sea. It’s just seemingly endless and it’s really gorgeous. If you go there during the times that they’re tolerating drought, there’s not much going on. But if you go during the wet portion of the spring, they’ll be really lush. There’s tons of plant and animal biodiversity in sagebrush systems. You go there, and there’s so much smell going on. You can almost touch it, it’s so thick, and it’s a wonderful sensory experience. 

Science Moab: What makes sagebrush such a drought-tolerant plant?

Mahood: Sagebrush has actually two types of leaves. There’s the big three-lobed tridentata leaf, and then smaller leaves pop out when there’s moisture, so it has perennial leaves and deciduous leaves. It also just has really deep roots, like many desert plants. So that’s another way that it survived long periods of drought: tapping into deep water sources.

Science Moab: What’s happened to sagebrush since colonization of the West? Have invasive species been an issue for it?

Mahood: In the early to mid-1800s, white people started coming across the Western US. It was this unchecked, unmanaged situation where people just grazed as many cattle as they could. With that also came the spread of a lot of invasive plants, in particular cheatgrass. It’s definitely helped by the breaking up of the crust. Cheatgrass has adapted to follow humans around. Humans break up the soil, trample it, and then have a bunch of seeds stuck to our shoes. And then those seeds are adapted to that loose broken up soil. It’s the same thing with cattle. Cheatgrass has a particular shape that lends itself really well to sticking in your shoes and the lower legs of cattle. And there’s that trampling and cheatgrass just does really good in trampled soil.

Science Moab: Why is cheatgrass so threatening to the sagebrush?

Mahood: This whole sagebrush-cheatgrass thing is a classic example of changes in ecosystem structure leading to changes in ecosystem function. The cheatgrass invades the sagebrush ecosystem and fills in the gaps, so you’ll see these pictures of sagebrush shrubs and there’s just a solid layer of cheatgrass in between them. Once they burn, cheatgrass seeds have fire-induced germination cues. After the fire, there’s the dispersal from cattle, the germination cues, and another thing that cheatgrass does: it grows really fast in spring. Sagebrush just can’t compete with its ability to capture spring moisture, until the combination of all those forces leads to an unstable plant community for a couple of years. After like three or four years, it settles into just being this monoculture of cheatgrass and a couple of forbs. And once it’s just this bed of really flammable fine fuel, it becomes really susceptible to fire, so you have this thing called the grass fire cycle. We’re kind of changing from a desert scrubland into an annual grass savanna.

Science Moab: What management styles are being used to protect against invasives?

Mahood: There’s a lot of competing forces. There’s some thinking sagebrush should be less dense and there should be more perennial grasses growing between, more of a grassy shrubland. That’s probably what it used to look like, a lot more perennial grasses in there. People are trying to do things to thin it out, like creating fuel breaks in the sagebrush to try to prevent it from burning. But then there’s unintended consequences: if you just cut a big line in the sagebrush, you might just introduce a bunch of annual grasses and the break becomes more flammable than before. That’s an area of ongoing research; people aren’t really sure exactly the best way to save the sagebrush. Even if it’s not invaded by cheatgrass, if you just have a wet year, the native stuff that’s already there will kind of join the fuel enough to get a big fire in there. And it definitely doesn’t come back except at higher elevations, but the low elevation stuff is definitely imperiled.

Science Moab: How have restoration efforts gone? What new strategies are being developed?

Mahood: The restoration of sagebrush has not been a huge success. Trying to actually do effective restoration in sagebrush is another area of active research that people are doing some really good stuff on. For a long time, management agencies would just do one-off aerial seeding, which typically hasn’t really worked that great. It’s a lot more expensive to plant live containerized plants, but they have a higher probability of survival. So there’s strategies of planting clusters in ideal areas, finding little nooks where it’s a little wetter, then planting clusters to try to create a seed source. Before sagebrush burns, each shrub is a little island of fertility, so the soil underneath has way more nitrogen and phosphorus and carbon. And then in between, it’s clay with very beautiful soil crust on top of it. After a fire, those little islands of fertility actually are still really fertile. So if you go and plant where those little fertile Islands are, there is a much bigger chance of getting things to take hold.